Katie Mason

Vet Katie Mason checks a cow.

Two main measures of milk yield will determine how well a cow produces: her peak lactation yield and her ‘persistency’ of milk yield. As we pass peak lactation and move into mid lactation, the aim is to promote persistency of milk production, in other words to encourage cows to produce as much milk for as long as possible.

Traditional pasture-based systems are ‘matched’ such that peak lactation in October largely coincides with the most plentiful and highest-quality pasture, but how do we ensure cows maintain lactation yields through the mid and late season?

After reaching peak lactation (about for-six weeks after calving), the cow’s appetite is at full capacity to be able to consume all the nutrients required for production, providing the diet is of high enough quality. A high quality and plentiful diet is important in mid lactation to sustain production. In late lactation the energy required for milk production declines, but high quality energy-dense feed is still required for pregnancy and increasing body condition score for the next lactation.

Total milk yield (peak and persistency) is determined by a number of factors:

  • body condition score at calving
  • peak milk yield itself i.e. how much the cows produced at peak
  • nutrient intake following peak yield
  • other factors such as disease status and climatic stress such as heat stress in the summer which may depress dry matter intakes
  • genetic factors – ‘persistency’ of milk yield is heritable but not as highly heritable as peak milk yield.

Many of the things listed above, have already been predetermined by the time mid lactation comes around so it becomes important to focus on the factors within your control like nutrient intake and disease status. If mineral deficiencies (such selenium and copper) have not been checked by blood or liver sampling and corrected prior to mating, then this should be addressed now.

In New Zealand dairy cows the rate of decline of milk production from peak is about 7-8% by month, but this can range significantly from between 3% and 4% per month to 12% per month. As well as reducing milk production; poor feeding can also cause cows not to cycle for many months. It is not uncommon to find herds where a high number of empty cows at pregnancy testing have not shown signs of heat.

Cows will also dry themselves off prematurely if they receive insufficient nutrients to maintain milk production.

Since high quality and plentiful feed are paramount to maintaining milk production, frequent farm walks and measuring of pasture residuals and intakes is key. DairyNZ’s quick nutritional checks are useful:

  • check your pasture residuals before and after every grazing
  • monitor daily milk solids yield and milk fat and milk protein trends
  • check your cows are eating the supplements you offer.

Pasture round length needs to be carefully considered, particularly in changeable weather, to avoid under or over allocating pasture. Under-allocating pasture and restricting pasture allowances to less than cow requirements can cause significant drops in milk production. Try also to avoid over-allocating pasture as residuals of more than 1500kg drymatter (DM)/hectare will reduce subsequent pasture quality and regrowth potential.

Returns on supplementary feeds will also be compromised when residuals are greater than 1500kg DM/hectare. A useful resource for assessing supplementary feed return can be found at: https://www.dairynz.co.nz/feed/supplements/supplement-price-calculator/

Assessing your herd’s performance and observing trends is key.

Are your cows declining in milk production by 7% or more by month between November and January?

Is total milk solid yield declining rapidly over a 10-day period? This could be an indication that cows are insufficiently fed.

Is milk fat percentage increasing? This may mean that cows are mobilising body fat stores and losing body condition due to insufficient intakes or pasture quality is declining?

Is milk protein percentage declining?

Close observation of these trends can allow you to remedy the situation early and promote a lengthy lactation with a slow decline in milk production.